Selector system for radio receiving apparatus



L. L. JONES March 22, 1932.

SELECTOR SYSTEM FOR RADIO RECEIVING APPAATUS Filed Jlly l5, 192'."

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Ill'- libllll l M NU Patented Mar. 122,* `1932i *LESTER L. Jonsson onaniiifi.,4 NisWaERsEY4 y l snLncToRsYsriiivr non :annie RECEIVING vAzeriii'iiiriis-l .appiicaamnA ineaA July I15,

This invention relates to a radio receivingl apparatus and relates more particularly to radio receiving apparatus embodyiiigseparate selective and amplifying systems whereby the selection' of the electrical oscillati'ons of a desired frequency is accomplished prior to amplificationtliereof, and has special reference kto thel provision of yan improved system, for effecting geometric '1 selectivity of the electrical oscillations of the f desired frequency.

A prime Idesideratum of my present iii-` vention centers about the provision of a radio receiving apparatus'in Whichtlie selection of the desired frequency is accomplished in geometric progression by means of three or f more tuned circuits arrangedin cascade, said circuits being ldevoid of separate energy sources so that the selection of the oscillations of the desired frequency is accomplished Without energy amplification or relay action,

this selective system being so organized that. the full geometri'cselectivity of the system` is realized or effectuated.

A further prime desideratum of my present invention relates to the provision of a system for geometrically selecting the electrical oscillations of ak given frequency from i oscillations diering therefrom in frequency embodyingthree or more tuned or selective circuits arranged iiicascade and adapted for association with an electrondi'scharge device amplifying system, the selector system `being organized and constructed to secure a maximum selectivity .of the system With a Y minimum loss of ,energy in transmitting the selected energy vthrough the system.

As is Well known the most common type of lector and energy amplier of the signalfimpressed upon the energy receptor or antenna.

. of the energy through each ofthe cascaded I have further Vdiscovered vthat these circuits..

1927. seriai'NQ. 205,935.

Thebuilding or constructingof a tuned radio, Y frequencyreceiver, throughout the develop-kr ment of the art, has been beset With numerous ditiiculties requiring scientific and engineering development; and such diiiicultieshave l increased from timeto time vras the art prof gressed as it became necessary to build radio receivers of exceedingly high selectivity and sensitivity. The diiiiculties encountered have multiplied geometrically lWith the number of timed stages required so thatk the physical limitations of timed radio frequencylreceivers imposed a limit to the selectivity and sensitivity achievable. F u By my present invention I propose todeviate from this'prior practice of cascadingL tuned radio frequency audion stages wherein the selectivity and amplication of the energy are simultaneously accomplished, and I pron pose to utilize separate instrumentalities or systems for accomplishing the selection of the frequencyand theY amplification of the energy, these separate selector andy amplifying systemsfunctioning to produce a highpowered receiver of great selectivity. To accomplish this obj ect I f have found vthat the selector system, devoid of electron v, discharge devices or separate energyv sources, should be organized so as to constrain the flow 0 circuits of the selective system, the said circuits being'furthermore so interrelated as to prevent any but the first circuit of the series to receive energyfrom ain/extraneous source.

of the selective system may be so operated as to effect asmaximum transfer of energy with a minimum energy loss in the transmission of the energy; and that When so organized a Y maximum aiidfull geometric selection of the energy` is eiected., ,'A selective system embodyin'g organized circuit instrumentalitiesV for accomplishing thesey results forms the sub-k ject matter of the present application. n n

I have further discovered that to produce a successful radio receiver in which the frequency selecting equipment or system is sepa-- rated from the energyainplifying system, the amplifier of the audion or electron discharge tube type) must be designed so as yto prevent any disturbing reactions from reaching the selector system, such disturbing reactions having the effect of destroying the selective functioning of the selector system, and that such an amplifier must be associated with the selective system to operate upon only the selected energy coming from the selector system. This interrelation between the selective system and the amplifying system is described generally in the present application, but is more specifically described andA broadly claimed in my copending application filed herewith, Serial No. 205,934 of July 15, 1927.

To the accomplishment of the foregoing and such other objects as will hereinafter appear, my invention consists in the elements and their relation one to the other, as hereinafter more particularly described and sought to be defined in the claims; reference being had to the accompanying drawings which show the preferred embodiment of my invention, and in which:

Fig. 1 is a Wiring diagrammatic View showing the combination of the selector and amplifying systems forming a radio frequency receiver, and j Fig. 2 is a diagrammatic view ofv a. modification thereof.

Referring'now more in detail to the drawings and having reference first to Fig. 1 thereof, the radio receiving system of my invention comprises a selective system generally designated as S and also by the legend Selector and an audion amplifying system generally designated as A also designated by the legend Amplifier, the selector system S comprising at least three circuits in cascade tunable to effect geometric selectivity, and the amplifier A comprising untuned audion or electron discharge tube stages coupled to the last selective circuit of the selector system S.

The selector system S comprises more specifically three or more tuned or selective circuits Sl, S2 and S3 kcoupled together preferably inductively by variable coupling means referred to more in `detail hereinafter, the first selector circuit S1 being coupled to an energy receptor such as the antenna ay and the last selector circuit S3 being coupled to the filament grid circuit of the first tube of the amplifier A.

I have found that in order to realize the full y geometric selectivity of the selector system S, the selective circuits S1, S2 and S3 thereof must be so yinterrelated that the first and third circuits S1 and S3 must be capacitively decoupled and inductively decoupled so that the energy transferred from the first to the third selectivecircuitsof the series is constrained to flow through the second or intermediate circuit S2ofthe series. Thethreeor more cascaded selective circuits should be capac? this shielding also insures that the second and third selective circuits S2 and S3 are prevented from receiving any extraneous energy. This intercircuit shielding or decoupling except for the energy coupling means etween the circuits is very important in order to realize the full selectivity of the system, this being evident when it is considered that if it were possible for circuit S1 to induce a part of its energy directly into circuit S3,

theselectivity of the circuit S2 would be eliminated as a factor in the selectivity of the system. This condition is more severe than in ordinary tuned radio frequency circuits since there are no separate sources of energy in the selector system S and therefore the energy received by the circuit S3 is of the same order of magnitude as that transmitted from the selective circuit S1.

The selector circuits S1, S2 and S3 each comprises a tuning element preferably in the form of a condenser designated as C with an exponent corresponding to the circuit of which it forms a part, and an inductance designated as I also with an exponent corresponding to the circuit of which it forms av part, the capacitive and inductive components of each of the circuits being arranged in series, as clearly shown in the drawings. The antenna a is coupled capacitively by means of the condenser 10rto the first tuned circuit S1; andwhere the tuning condensers C', C2 and C3 are desired to be simultaneously adjusted for unicontrol, the additional capacity added by the antenna a and its coupling condenser 10 is made equal to the tube input capacity effective on the selective circuit S3, and ya small fixed condenser 11 equal to this capacity is placed in shunt with the variable condenser C2 of the circuit S2.A

The circuits of the selector system are preferably coupled to each other inductively and adjustably, this being accomplished by means of the coils 12 and 13 which are adjustably coupled to the inductance coils I2 and I3 respectively, the adjustment of the coupling being indicated by the arrowed lines 14 and 15 respectively. These coupling'means are so constructed as to permit a coupling range from zero coupling to a maximum coupling which is nevertheless a loose coupling, i. e., to a coupling value just short of what will produce coupling waves inthe circuits, that is, double resonance peaks. As is well known, a single resonant circuit has a single resonance peak.v If two such similar circuits are inductively coupled together with a very slight coupling, their combination also has a single resonance peak. If the coupling is increased or tightened, the single resonance peak first broadens and then divides into two distinct and separated resonance peaks, corresponding to frequencies higher and lower than the resonance frequency of the` single circuits, which condition is obviously very undesirable in 'a selector. In ordinary technical parlancey couplings permittingthe retention of a single resonancepeak are considered to be loose close couplings.l In the present selector the` maximum coupling is less than a close coupling, and does not produce a-double resonance peak. This double resonance phenom-l enon, and the energies of different frequencies tendingto result therefrom, are frequently y'referred to as coupling waves. Y

To capacitivelyv and inductively shield or 1 decouple the circuits except for the adjustable 'energy coupling means 12-Iv2 and 13-7-I3, the main r`inductances I', I2 and I3 are f made astatic, these inductances being either of the binoculartype or of thexconc'entric astatic type described and claimed in my patent to acoil system, .1,608,560-of November 30, 1926, the construction being such that there is freedom ,from magnetic and electrostatic coupling between these inductances. The condensers of the circuit are preferably of the grounded rotor typey so that there Iis freedom from inter-capacitive coupling between these elements. `The low potential side `of eachr selective circuit is grounded as at 16, 17 and 18 respectively, and eachv of theA circuits is made highly efficient by the use of Litz wire coils and dielectric mountings of low loss. I have found this construction sufficient to accomplish the desired end, but if desired each circuit may be arranged in a separate metal compartment. i I 2 By the provision of this construction I have determined that each of the selective circuits iscoupled to the othery only through the'adjustable energy coupling means therebetween, this being diagrammatically represented yby the broken dotted line 19 inFig. 1 of the drawings. When the circuits are so constructed each of the three or more tuned circuits of the series contributes its share to y'and forms afull component in the selectivity of thesystem since that coupling between a circuit and anon-adj acent circuit whichresults in virtually eliminating an intermediate circuit of the series as a selector component is effectivelylector system, the coupling instrumentalities e 12-I2'1and 13-I3 are adjustable/so as .to equalize the selectivity of all'of the circuits of ythe series, this being accomplished byl constructing the adjustable coupling instrumenta-lities for simultaneous and similar op- .Y eration.A This is diagrammatically represesentedv by the single dialA element 2O which is coupling inductances 12 and 13 to effect the simultaneous operation of the latter.`

By similarly adjusting the coupling instrumentalities there is prevented a difference in degree of coupling between the circuits S1.

S2 and the circuits S2, S3, such difference in degree resulting in a loss of selectivityof the system. This will be seen when itis appreciated that when a pair of the circuits are more tightly coupled thananother pair, the loss ink selectivity of the system due to the tightly coupled pair is greater than the gain in selectivity which is,r due to the weakly coupled pair, so that for a given energy transmissionvthe selectivity of the system as a whole is less than it would be where both pairs of circuits arev coupled with equal similar and preferably simultaneous adjust-r ment is made of the energycoupling means therebetween, provides a successful solution of the problem of building a selector system which is adapted to produce true geometric selectivity and which is adapted for circuit attachment to a separate audion amplifierl of the untuned type.

In order to makethis selective system S functionable in a radio receiving system, I have discovered that it must lbe associated with an amplier of proper characteristics, y

the amplifier being designed so as t0 inhibitany reactions upon the selector system which ytend to destroy the selectivity thereof, andsc as to prevent the pickingup of any energy' except that fed to the amplifier through the selector system. Such an amplifiershould also desirably be sulhciently powerful to in# crease the signal to a volume suitable for operating the audio system even though the i couplings in the selector systembe made quite loose so as to permit said loose couplings to be used and realize the full geometric selectivity of the system.

To accomplishthese results my inventionV is` directed to the provision of an amplifier embodying a series of electronL discharge tubes and having a pair of tubes first in the series which are so organized asto eliminate all damping reactions and oscillating creat ing tendencies atk the input terminals of the rst tube of the series. I have discovered that in the prior art amplifying systems there existed a transition from an unstable oscilla the selector system; and therefore to elimi-y nate these reactions and the transition from an oscillatory condition to a damping reaction, the cascade audion amplifier A is equipped with a pair of tubes T1 and T2 respectively of the triode or three-electrode type coupled together and to subsequent circuits in such a way as to eliminate or balance all of the reactions at the input terminals of the tube T1.

The specific functional interrelation of the parts of this amplifier system is more particularly described and claimed in my aforementioned copending application filed concurrently herewith, Serial No. 205,934; and in the present application I will confine the description of this amplifier to the structural features and broad functional interrelation of the pair of coupling amplifier tubes T1 and T2.

Each of the tubes T1 and T2 comprises the usual grid, plate and lilament, g, 2), and f respectively, the filaments of the tubes being connected b means of filament circuits to ythe A battery esignated -A+. Both filament circuits may be suitably provided with fixed resistors such as r, r. The B battery designated *B+ is connected in the usual way to the A battery and to the output circuits of each of the tubes T1 and T2, a blocking condenser 21 being employed connecting the plus side of the B battery to the minus side of the A battery. The input and output circuits z", o', 2, 02 of the tube stages T1 and T2 are connected as clearly shown in the drawings.

To balance the reactions at the input terminals of the input circuit z", the circuit net-v work of the amplifying tubes T1 and T2 are, generically speaking, so organized as to cause such network to act or behave as 4a pure reactance, either capacitive or inductive. To

ermit of uni-control for the selective system b, this amplifier circuit network should further be so designed as to produce a constant reactancc at the input terminals of the first input circuit i. plified in Fig. 1 of the drawings, this reactance is capacitive. IVhen the circuit network of the amplifier A is made to react as a pure capacitance (all positive and negative resistances effective on the input circuit c" being elminiated for the whole wave length range) I have found that the selectivity of the-selector' system S is unimpaired and is capable of optimum operating results; and when such a capacitance is maintained constant,

e uni-control of the selector system S may be accomplished.

To attain this balance at the input ter- In the construction exem-r neueresminals of the' first tube T1, I first fix the constants of the output circuito in accordance with the principles described and claimed in my copending application, Serial N o. 51,569, August 21, 1925, or in my Patent 1,620,661, March 15, 1927, the natural frequency of this output circuit in connected circuit being greater than the highest frequency of the whole frequency range through which the input circuit z" is tunable. Vith this characteristic, feedback reactions from the output circuit 0 to the input circuit 1l are produced for the whole frequency ranfre, which feedback reactions are neutralized by means of a resistance R located in this output circuit and preferably between the plate and the inductive component of the output cirf cuit. This resistance may be of the order of 1600 ohms and is selected in accordance with the laws or rules described, for example, in my aforementioned Patent 1,620,661.

The output circuit 0 with these determined characteristics is then coupled tothe input circuit 'i2 by means of a coupling condenser K and an inductance M, the condenser K being tapped at a mid-point of the resistance R, the capacity K and inductance M when taken in series having preferably a natural frequency lower than the lowest frequency of the frequency band to be transmitted through the amplifier. Preferably also, the plate side of the resistance R is shunted by means of an inductance N and a condenser D. The inductance M may be loosely coupled to the plate inductance L, but preferably is closely coupled thereto.

As an example of suitable magnitude of these constants, the section of resistance R between the plate and the intermediate tap may be 921 ohms, the remainder of the resistance R about 707 ohms, the coupling condenser K, 250 micromicrofa-rads, the inductance N, 22-microhenrys, and the capacity D, 150 micromicrofarads. The inductance M isy preferably divided into two sections, one transformer coupled to the inductance L and the other a free section, the free section being about 480 microhenrys and the coupled section about 150 microhenrys. The transformer coupled parts are preferably bifilarly wound after the manner described and claimed in my copending application, Serial No.'195,631 of June 1, 1927, for transformer and coil system.

To balance the aforesaid reactions over the whole wave length range, I have found that the effective input capacity at the input terminals of the circuit 2 should rise in a predetermined way with increase of wave length. This I accomplish by predetermining the characteristics of the transformer sv in the output circuit o2 of the tube I have found that this transformer should be'given a natural frequency lower than the lowest frequency of the range of the receiver,

w ing'input capacity characteristic at the input terminals vof the second circuit 2;- lThis transformer p', s is also preferably of the biiilarly wound type, tlienatural frequency of which is selected to be about 625 meters. i

By the provision of this-construction *Il therefore first stabilize; the adjacent stage reactions of the tube T1, then neutralize the feedback reactionsbetween these stages and.

finally impose a. varying input capacity characteristic on the input of the second tube T2 by predetermining the characteristic of the output circuit of the tube T2;A and by this combination vofmeansk I balance over the whole wave length range the feedback and feed-forward reactions at the terminals of the first tube T1.

rlhe amplifying system A" isv desirably shielded as by an enclosing shield 23 so that the same is prevented'from picking .up anyk energyexcept that received from the selector system S.

In F ig. 2 of the drawings I show a modified form of the selector system of the radio rfrequency apparatus ,wherein three instead of two adjustable coupling means is employed. Otherwise, the circuits are substantially similar to those showninFig. 1 of the drawings. In this modification the selector system S' comprises the three selective circuits S1, S12 and S3, similar to those heretofore described, the circuit S1 including a thirdy adjustable coupling instrumentality generally'design ated as 22 which couples the circuit S1 inductively to the` receptor or antenna a. This adjustable couplingmeans 22 is connected to the other adjustable elements 12 and 13 so that all are simultaneously adjustable Y by means of the single dialQO. The remaining parts of the selector system Slof'Fig. 2 are substantially similarto those shown in Fig. 1 and are indicated ,by similar reference numerals.

The operation of the radio apparatus and the selector system therefor of my present invention, and-the many advantages thereof, will, in the main, be fully yapparent from the above detailedvdescription thereof. It will also be apparent that while I have shown and described my invention in the preferred form, many changes and modifications may be made in the structure disclosed without departing from the spirit of the invention, defined inthe following claims;`

' I claim:

1. A system for geometrically selecting electrical oscillations lof a given frequency from 'oscillations differing therefrom in frequency comprising atleast three efficient circuits each including capacitive and inductive reactances and being adjustably tunable to the frequency of the oscillations to be selected and arranged in cascade or series, a first coupling means linking the first circuit of the i series to the second circuit for thek transfer to the second circuit of energy selected by the first circuit-,a secondv coupling meanslinking the second 'circuit'of the series to the third circuit for thetransfer to thev third circuit of energy'selected by thek second circuit,l

the coupling beingfless than that producing couplingwaves, means for grounding one side of each of said circuitsbetween thek capacitive and inductive reactances thereof,

and means for capacitively and inductively decoupling the 'first and third circuits yof thek series from each other whereby theenergyy transferred from thefirst to the third circuits .of the series is constrained to iiow through the secondy or intermediate circuit of the series.

2. A system for ygeometrically selecting without energy amplification electrical oscillati ons of 'a given frequency from oscillations differingtherefrom in frequency comprising at least three efficient circuits resonant to the frequency of they oscillations to be selected 1 and arranged in cascade or series, variable capacitive means in'eachl of the circuits for tuning thefsame to resonance, a first inductivek coupling means linking the first .circuit ofthe series to thel second circuit for the transfer tothe second circuit of energy selected by the first circuit, a second inductive coupling.

means linking the second circuit of the series to the third circuit for thetransfer t0y the third circuit of energy selected by the second circuit, the coupling being less than that producing coupling Waves, means for grounding one side of each of said circuits between the capacitive ,and inductive reactances thereof, and meansr for capacitively and inductively decoupling the first and third circuits of the series from each other to a high degree where-k by the energy transferred from the first to the thirdcircuits of the series is contrained to iow through and be selected by the second or intermediate circuit of the series.

3. A systemfor geometrically selecting` electrical oscillations of agiven frequency from oscillations differing therefrom in frequency comprising at least three efficient cir-` cuits each includingcapacitive and inductive reactances and being adjustably tunable to the frequency of the oscillations: to be selected and arranged in cascade or series, a first coupling means linkingthe first circuit of the series to the second circuit for thetransferto the second circuit of energy selected by the first circuit, a second couplingmeans linking l me side of each of said circuits between the capacitive and inductivel reactances thereof,

and means for capacitively and inductively `whereby the energy transferred through the three circuits of the series is constrained to fiow. solely from a circuit to its next adjacent circuit and only through said coupling means.

4. .A system for geometrically selecting electrical oscillationsof a given frequency from oscillations differing therefrom in frequency comprising at least three efficient circuits each including capacitive and inductive 4, reactances and being adjustably tunable to the frequency of the oscillations to be selected and arranged in cascade or series, a first adjustable coupling means linking the first circuit of the series to the second circuit for the vtransfer to the second circuit of energy selected by the first circuit, a second adjustable coupling means linking the second circuit of the series to the third circuit for the transfer to the third circuit of energy selected by the second circuit, the maximum coupling kbeing less vthan that producing coupling waves, means for grounding one side of each of said circuits between the capacitive and inductive reactances thereof, means for capacitively and inductively decoupling the first and third circuits of the series from each other so that the energy transferred from the first to the third circuits of the series is yconstrained to flow thnoughthe second or intermediate circuit,

and means for varying both of the adjustable coupling means to produce substantially like degrees of coupling therein. l

5. A system for geometrically `selecting without energy amplification electrical oscillations of a given frequency from oscillations differing therefrom in frequency comprising at least'three efficient circuits resonant to the frequency of the oscillations to be selected and arranged in cascade or series, rvariable capacitive means in each of the circuits for tuning the same to resonance, a first variable inductive coupling means linking thefirst circuitof the series to the second cira cuit for the transfer to the second circuit of energy selected by the first circuit, a second variable inductive coupling means linking thesecond circuit of the series to the third circuit for a transfer to the third circuit of energy selected by the second circuit, the

maximum coupling being less than that producing coupling Waves, means for grounding one side of each of said circuits between the capacitive andy inductive reactances thereof, means for capacitively and inductively decoupling the first and third circuits of the series from each other to a high degree so that the energy transferred from the first to the third circuits of the series is constrained to flow through the second or intermediate circuit, and means for simultaneously adjusting both yof vsaid coupling means to produce substantially like degrees of cou ling therein.

6. A system for geometrica ly selecting electrical oscillations of a given frequency from oscillations differing therefrom in frequency comprising at least three efficient circuits adjustably tunable to the frequency of the oscillations to be selected and arranged in cascade or series, a first coupling means linking the first circuit of the series to the second circuit for the transfer to the second circuit ofvenergy selected by the first circuit, a second coupling means linking the second circuit of the series to the third circuit for the transfer to the third circuit of energy selected by the second circuit, the maximum coupling being less than that producing coupling waves, and means for adjusting both of said couplingmeans to equalize the selectivity of all of the circuits of the series.

7 A system for geometrically selecting electrical oscillations of a given frequency from oscillations differing therefrom in fre-` quency comprising at least three efficient circuits arranged in cascade or series, tuning means for each of the circuits to render the same resonant to the frequency of the oscillations to be selected, a first adjustable coupling means linking the first circuit of the series to the second circuit for the transfer to the second circuit of energy selected by the first circuit, a second adjustable coupling means linking the second circuit of the series to the third circuit for the transfer to the third circuit of energy selected bv the second circuit, the maximum coupling ing less than that producing coupling Waves, and means for simultaneously varying both of said coupling means to produce substantially like degrees of coupling therein.

8. A system for geometrically selecting electrical oscillations of a given frequency from oscillations differing therefrom in frequency comprising at least three efficient circuits resonant to the frequency of theoscillations to be selected and arranged in cascade or series, a first adjustable coupling means linking thefirst circuit of the series to the second ,circuit for the transfer to the second circuit of energy selected by the first circuit, a second adjustable coupling means linking the second circuit ofthe series to the third circuit for the transfer to the third circuit of energy selected by the ysecond circuit, the maximum coupling being less than that producing couplings Waves, and means for simultaneously and similarly adjusting both of said coupling means.

9. A system for geometrically selecting electrical oscillations of agiven frequency from oscillations differing therefrom in frequency comprising a plurality of efficient circuits each adj ustably tunable to the frequency of the oscillations to be selected and arranged Y of said circuits, shielding for said circuits,

' the circuitsand shielding and coupling means being suchfthat solely each of the said coupling means is eective for transferring energy selected by one circuit to a circuit next adjacent thereto, and means for varying at least two of said coupling means to produce substantially like degrees of couplingtherein.

10. A system for geometrically selecting electrical oscillations lof a given frequency from oscillations diiering therefrom in frequency comprising a plurality of efficient circuits each resonant to the frequency of the oscillations to be selected and .arranged in cascade or series, al plurality of adjustable coupling means linking the said circuits together, the maximum coupling being less than that producingcoupling waves, an energy receptor, means loosely Coupling the same Vto the first of said circuits, shielding for said circuits, the circuits and shielding and cou pling means being such that solely each of the saidcoupling means is effective for trans- -ferring energy selected by'one circuit to a circuit next adjacent thereto, and means for simultaneously and similarly adjusting at least two of said coupling means.

l1. A system for geometrically selecting electrical oscillations of a given frequencyy from oscillations differing therefrom in free quency comprising at least three efcient circuits eachv including capacitive and inductive reactances and being resonant to the frequency of the oscillations to be selected and arranged in cascade or series, a small portion of the inductance of the first circuitof the series being coupl-ed to the main inductance of the second circuit for the transfer to the second circuit of energy selected by the first circuit, and a Vsmall portion of the inductance of the second circuit being coupled to the main inductance of the third circuit of the series for the transfer to the third circuit of energy selected by the second circuit, the coupling being less than that Vproducing couplingvwavesmeans rfor grounding one side of each of said circuits between the capacitive and inductive reactances thereof, and means for capacitively and inductively shielding the first and third circuits of the series from each other to inhibit any transfer of energy therebetween, whereby the energy transferred from the first to the third circuits of the series is constrained to flow through the second or intermediate circuit of the series. l Y

12. A system for geometrically selecting b electrical oscillations ofV aV given frequency from oscillations differing therefrom in frequencycomprisin'g at least three efficient cir.-y cuits each including ycapacitive and inducetivereactancesV and being resonant to the frequency ofthe oscillations to be selected and arranged in cascade or series, a small portion ,of the inductance of the first circuit being coupled to the main inductanceof the second circuit :of the series for the transfer to the second circuit of energy selected by the first circuit, vand a small portion of the inductance of the secondvcircuit kbeing coupled to the main inductance of the third circuit of the series for the transfer to the third circuit of energyy selected Aby the second circuit, the maximum coupling being less than that producing coupling Waves, means for grounding one side of each of said circuits between the Y capacitive and inductive reactances thereof, means for capacitively and inductively shielding the first and third circuits ofthe degree any transfer of energy therebetween whereby the energy transferred from ythe first to the thirdkr circuits Vof the series is constrained to iow through the second or inter-y ka5 series from each other to inhibit to a highy mediate circuit of the series, and means for Y varying the coupling between thefirst and second circuits and between the second and third circuits simultaneously.

13. Asystem for geometrically selecting electrical oscillations of a given frequency from oscillations differing therefrom in frequency comprising at least three eflicient circuits adjustably tunable to the frequency of the oscillations to be selected and arranged in cascade or series, a first coupling means linking the first circuit of the series to the second circuit vfor the transfer to the second circuit of energy selected by the first circuit, a second coupling means linking the second circuit of the series to the third circuit `for the transfer to the third circuit of energy selected by the second circuit, the coupling being less than that producing coupling waves, and means for capacitively and inductively decoupling the first land third circuits of the series from each yother to a high degree whereby the energy transferred from the first to the third circuits .of the series is constrained to flow through kin cascade or series,- a first coupling `means linking the first circuit of the series yto the second circuit for the transfer to the second circuit of,v energy selected by the rst circuit,

a second coupling means linking the second circuit of the series to the third circuit of energy selected by the second circuit, the coupling being less than that producing coupling waves, means for independently grounding each of said circuits, and means for capaeit-ively and inductively decoupling the first and'third circuits of the series from each other to a high degree whereby the energy transferred from the first to the third circuits of the series is constrained to How through the second or intermediate circuit of the series.

Signed at New York, in the county of New York and Sta-te of New York, this 11th day of J uly, A. D. 1927.

LESTER L. JONES. 

